PROJECT SUMMARY In this project, we will employ a new model of urinary tract infection (UTI) in female and male mice to illuminate the influence exerted by androgens on susceptibility to, and severity of, these infections. Prior studies of the influence of sex hormones on UTI have been limited to estrogen exposure only. However, our recent findings indicate that the influence of sex, particularly androgen exposure, on these common bacterial infections is more complex than previously appreciated. Until now, sex differences in UTI pathogenesis and host response have not been examined in preclinical models, largely because technical (anatomic) considerations preclude routine catheterization of the male mouse bladder. Thus, preclinical modeling of bladder infection (cystitis) and kidney infection (pyelonephritis) has previously been performed almost exclusively in female mice. In response to this deficit, we recently developed, optimized, and published a novel, innovative, minimally invasive surgical bladder inoculation technique that allows first-ever studies of sex differences in UTI pathogenesis and host response. Our method of direct bladder inoculation with uropathogenic Escherichia coli (UPEC), which bypasses traditional anatomic differences between sexes, has already revealed strikingly higher susceptibility of male and androgenized female mice to chronic cystitis, severe pyelonephritis, ascending renal abscess formation, and tubulointerstitial fibrosis. These findings correlate with epidemiologic data revealing higher morbidity and mortality in men who do suffer complicated UTI (compared with women), and higher incidence of UTI in women with a common hyperandrogenic condition (polycystic ovary syndrome). On the basis of these findings, we hypothesize that androgens enhance epithelial receptivity to uropathogenic bacteria and/or influence the host immune response to bacterial infection of the urinary tract in both female and male hosts. To interrogate this hypothesis, we propose to first prove that the observed phenotypes arise from signaling through the androgen receptor; this will involve female mice androgenized with DHT (a specific AR agonist) as well as pharmacologic AR inhibitors. Next, we will define and interrogate androgen effects on both the soluble and cellular components of host immune responses to bladder and kidney infection, using a variety of techniques and newly generated C3H/HeN conditional AR knockout mice. Finally, we will take multiple in vitro and in vivo approaches to defining androgen effects on uroepithelial biology and interactions with uropathogenic bacteria. Our results will illuminate the influence exerted by androgens, in both female and male hosts, on pathogenesis and host response in both lower and upper-tract UTI. In addition, our preclinical findings will also be translationally relevant to UTI risk in multiple human patient populations, including otherwise healthy women.